The Stop 0x79 message indicates that the hardware abstraction layer (HAL) and the kernel type for the computer do not match. This error most often occurs when ACPI firmware settings are changed. For example, you might install Windows XP on an x86-based computer with the firmware ACPI enable option enabled and later decide to disable it. This error can also result when mismatched single and multi-processor configuration files are copied to the system.
• A Stop 0x79 message occurs when the system is using out-of-date Ntoskrnl.exe or Hal.dll files. This can occur after manual repairs that involve copying incorrect files to the system. This error also occurs when using mismatched files, such as copying a multiprocessor HAL on to a system using a single-processor kernel (or vice versa). The kernel and HAL files for single-processor and multiprocessor systems are stored on the Windows XP Professional operating system CD using two different file names. For example, the single and multi-processor versions of the kernel, named Ntoskrnl.exe and Ntkrnlmp.exe respectively. Setup copies either Ntoskrnl.exe or Ntkrnlmp.exe to your system as Ntoskrnl.exe. In Recovery Console, you can use the Copy command to copy the correct HAL or kernel files from the CD to the appropriate folder on the hard disk.
• If you experience Stop 0x79 messages after changing firmware settings, restore the original settings used during Windows XP Professional Setup.
Because systems that use the ACPI HAL ignore IRQ assignments stored in firmware, you can only manually change IRQ settings for non-ACPI (Standard PC HAL) systems. Some x86-based provide the option to toggle ACPI functionality. To disable or re-enable ACPI, you must change firmware settings and reinstall Windows XP. Because of the numerous registry and system file changes required, you must run Setup again (an upgrade installation does not work).